How do I print a returned variable calculated in another function?

[RedSkeleton007]

Hi all. My comprehension of how to use scope is not clicking. From the following code:

#!/usr/bin/env python3
#PracticePythonExercise01.py

#Create a program that asks the user to enter their name and their age.
#Print out a message addressed to them that tells them the year that they
#will turn 100 years old.

def yearThatYouTurn100():
    name = input("Enter your name: ")
    age = int(input("Enter your age: "))
    year = int(input("Enter the current year: "))
    yearsBefore100 = 100 - age
    yearAt100 = year + yearsBefore100
    return yearAt100

def main():
    yearThatYouTurn100()
    print(yearAt100)

main()

I get the error:

Error:
>>> ================================ RESTART ================================
>>> 
Enter your name: sam
Enter your age: 30
Enter the current year: 1988
Traceback (most recent call last):
  File "F:/Python/Python36-32/SamsPrograms/PracticePythonExercise01.py", line 20, in <module>
    main()
  File "F:/Python/Python36-32/SamsPrograms/PracticePythonExercise01.py", line 18, in main
    print(yearAt100)
NameError: name 'yearAt100' is not defined
>>>

No I don't want to print yearAt100 in the function that calculated it, because I'm still struggling to learn why I can't get the main function to recognize it.